Supported chromia catalysts for oxidation of organic compounds - The state of chromia phase and catalytic performance

A series of 13 bulk transition metals oxides frequently used as components of full oxidation catalysts was tested in air oxidation of n-butane and ethylacetate (EA). Co3O4 Cr2O3 CuO and MnO2,displayed the best activity, about one order of magnitude higher than the others. Chromia displayed the highest CO2 productivity. The activity and CO2 selectivity of Cr2O3 catalyst deposited on mineral supports (SiO2, Al2O3, MCM-41) depended strongly on the supports nature, texture and chromia loading. XPS, EDAX, XRD, FTIR and TPR-TPO measurements displayed two forms of Cr3+-oxide on silica-supported catalysts: bulk alpha-Cr2O3 nanocrystals of 10-20 nm and a monolayer of chromia surface species chemically bonded to the support: -Si-O-Cr=O. The chromia nanocrystals detected by XRD displayed higher activity and selectivity in complete EA oxidation due to higher redox mobility of chromium cations on their surface compared with grafted chromium silicate species. The optimized Cr2O3/SiO2 catalyst showed high efficiency in wet oxidation of amino-3-phosphonopropionic acid, comparable with the best catalysts reported in the literature. (C) 2000 Elsevier Science B.V. All rights reserved.